1. Field of the Invention
The present invention relates to a method and an apparatus for driving an image sensor device wherein a plurality of sensing elements are connected in a matrix. More particularly, the present invention relates to a method and an apparatus for driving a contact image sensor device having the aforementioned construction.
Contact image sensor devices are used for small-size facsimile terminal equipment, bar code readers, and the like.
2. Description of the Related Art
Since a contact image sensor device can sense an image of objects without use of an optical system for reduction of the image, the length of an optical path can be so shortened that equipment comprising the contact image sensor device can be miniaturized. For this reason, recently, contact image sensor devices are widely used as an image sensing unit in small-size facsimile terminal equipment, a bar code readers, and the like.
Though various types of contact image sensor devices are known, the contact image sensor device which is referred to in the present invention is a type of sensor device, which comprises a plurality of photodiodes connected in a matrix and an equal number of blocking diodes one each provided with each photodiode to prevent a so-called crosstalk phenomenon, and wherein successive driving pulses are sequentially applied to the blocking diodes to readout electrical signals from the photodiodes.
This type of contact image sensor device has an advantage that both photodiodes and the blocking diodes can be constituted by diodes having the same construction, so that the degree of integration of the sensor elements can be increased.
The prior art with regard to driving the contact image sensor device is described, in Japanese Unexamined Patent Publication (Kokai) No. 59-67770. In this publication, intervals between successive driving pulses are not considered. Therefore, needless pulses appear at the leading edge and trailing edge of the driving pulses in addition to signal pulses caused by light signals from a document, and thus noise pulses are included in output signals from the photodiodes. These noise pulses are caused by transfer of electrical charge stored at junction capacitances of the photodiode and the blocking diode. This phenomenon is referred to hereinafter as "capacitance kick". These noise pulses caused by the capacitance kick make image information of the document incorrect, and lower the S/N ratio.